title: Trophic hierarchies illuminated via amino acid isotopic analysis.
abstract: Food web ecologists have long sought to characterize the trophic niches of animals using stable isotopic analysis. However, distilling trophic position from isotopic composition has been difficult, largely because of the variability associated with trophic discrimination factors (inter-trophic isotopic fractionation and routing). We circumvented much of this variability using compound-specific isotopic analysis (CSIA). We examined the (15)N signatures of amino acids extracted from organisms reared in pure culture at four discrete trophic levels, across two model communities. We calculated the degree of enrichment at each trophic level and found there was a consistent trophic discrimination factor (~7.6‰). The constancy of the CSIA-derived discrimination factor permitted unprecedented accuracy in the measurement of animal trophic position. Conversely, trophic position estimates generated via bulk-(15)N analysis significantly underestimated trophic position, particularly among higher-order consumers. We then examined the trophic hierarchy of a free-roaming arthropod community, revealing the highest trophic position (5.07) and longest food chain ever reported using CSIA. High accuracy in trophic position estimation brings trophic function into sharper focus, providing greater resolution to the analysis of food webs.
authors.affiliation: USDA-ARS, Madison, Wisconsin, United States of America ; Department of Entomology, University of Wisconsin, Madison, Wisconsin, United States of America.
authors.forename: Shawn A
authors.initials: SA
authors.lastname: Steffan
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Chikaraishi
authors.forename: David R
authors.initials: DR
authors.lastname: Horton
authors.forename: Naohiko
authors.initials: N
authors.lastname: Ohkouchi
authors.forename: Merritt E
authors.initials: ME
authors.lastname: Singleton
authors.forename: Eugene
authors.initials: E
authors.lastname: Miliczky
authors.forename: David B
authors.initials: DB
authors.lastname: Hogg
authors.forename: Vincent P
authors.initials: VP
authors.lastname: Jones
mesh_terms: D000596:Amino Acids / Q000737:chemistry* / Q000302:isolation & purification; D000704:Analysis of Variance; D000818:Animals; D001181:Arthropods / Q000737:chemistry*; D018554:Avena / Q000737:chemistry; D020387:Food Chain; D008401:Gas Chromatography-Mass Spectrometry; D007814:Larva / Q000737:chemistry; D009587:Nitrogen Isotopes / Q000032:analysis*; D027805:Phaseolus / Q000737:chemistry; D013045:Species Specificity; D029799:Vaccinium macrocarpon / Q000737:chemistry
chemical_list: D000596:Amino Acids; D009587:Nitrogen Isotopes